In known devices of this type, using properties of polarization of light, the detected signal (light intensity) is not proportional to the measured width (angle or position).
It is necessary to include a signal treatment step in the chain for measuring and amplifying from the system.
Other known devices are supposedly intrinsically linear.
Such is the case for optical sensors with digital coding and fiber transmission, which comprise a great number of optical fibers associated at various positions of the sensor; their resolution is naturally limited by the number of fibers in position.
Another known optical device for angle measurement uses absorption of a light ray through an absorbing filter having the shape of a crown of which the density depends linearly on the angular position; this device also has an optical reference system for the measuring chain based on the optical Wheatstone bridge technique (which is a publicly known technique, see, for example "une technique d'equilibrage dans les capteurs a fibre optique a intensite modulee", B. Culshaw et al., 2eme conference international sur les fibres optiques, 1984, p. 117, VDE-VERLAG GmbH Berlin). This device has a significant defect in that the light beam does not coincide with the axis of rotation of the filter. An important disadvantage thereby results. In addition, it uses fiber optic couplers, connecting four optical fibers, which become unstable in difficult environmental conditions (vibrations, temperature variations. . . ). These instabilities relate to variations of the overall distribution of light energy in the optical fibers. Finally, the level of losses in this sensor has led its inventors to use laser diodes instead of optical sources with a larger spectrum, with the result that laser granularity is produced at the level of the absorbing filter which strongly reduces its resolution and the reproducibility of the measurements.